Typically, for a physical layer of a portable internet system of an OFDMA scheme four ranging modes are defined, such as an initial ranging, a periodic ranging, a hand-off ranging, and a bandwidth request ranging. The bandwidth request ranging mode is used for a terminal to request a bandwidth to a base station, and the other ranging modes are used for power control and an uplink synchronization acquisition between the terminal and the base station.
Meanwhile, the ranging PN code used for a portable internet system of an OFDMA scheme is generated by a characteristic polynomial as shown in equation 1, and the number of ranging PN code symbols available in each ranging mode is determined at the time of establishing an initial system.G(x)=x15+x7+x4+x+1  (Equation 1)
The ranging PN code generator applies different initialization codes for different cells using cell ID numbers, which are expressed as a combination of “00101011” and 7 bits (i.e., [s6:s0]).
For example, for the 144-bit-long ranging PN code, 256 ranging PN codes in total may be used for all the ranging modes, and such ranging PN codes may be generated as follows.
First, one long sequence generated through first to (144*(K mod 256))-th clock outputs of the ranging PN code generator are equally divided into K number of 144-bit-long codes, and they are used as symbols for the initial ranging mode.
Another long sequence is generated through (144*(K mod 256)+1)-th to (144*((K+L) mod 256))-th clock outputs of the ranging PN code generator and it is equally divided into L number of 144-bit-long codes for usage as symbols for the hand-off ranging mode.
In addition, a further long sequence is generated through (144*((K+L) mod 256)+1)-th to (144*((K+L+M) mod 256))-th clock outputs of the ranging PN code generator and it is equally divided into M number of 144-bit-long codes for usage as symbols for the periodic ranging mode.
Finally, another long sequence is generated through (144*((K+L+M) mod 256)+1)-th to (144*((K+L+M+N) mod 256))-th clock outputs of the ranging PN code generator and it is equally divided into N number of 144-bit-long codes for usage as symbols for the bandwidth request ranging mode.
FIG. 1 illustrates a schematic diagram of an apparatus for generating a ranging PN code used for a wireless portable Internet system of an SSRG scheme.
As shown in FIG. 1, a ranging PN code generator having an initial value of [0, 0, 1, 0, 1, 0, 1, 1, s0, s1, s2, s3, s4, s5, s6] generates K, L, M, and N numbered PN codes for respective usage as symbols for the initial ranging, the periodic ranging, the hand-off ranging, and the bandwidth request ranging through receiving the maximum (144*((K+L+M+N) mod 256)-th clock signals and equally dividing the output PN code into 144-bit-long codes. Therefore, the ranging PN code generator shows a drawback of consuming a significant amount of time to produce codes appropriate for all ranging modes and requires a maximum (144*256)-bit memory to store the pre-produced codes.
Also, because the terminal may transmit all of the above-noted four ranging modes (initial ranging mode, periodic ranging mode, hand-off ranging mode, and bandwidth request ranging mode) to the base station, the ranging PN code generator should process the maximum 256 numbered ranging PN codes simultaneously according to the setting system parameter on receiving the PN codes of the four ranging modes from the terminal.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore, it may contain information that does not form the prior art that is already known in this country to a person or ordinary skill in the art.